Tourette Syndrome (TS) is a neurodevelopmental disorder characterized by vocal and motor tics, as well as premonitory urges, obsessions, compulsions and attention deficits. Current medications for TS reduce tic severity in some patients, but are ineffective against the most impairing TS symptoms and are associated with significant adverse effects. Thus, new medications that effectively target TS symptoms, but are less prone to produce deleterious side effects are critically needed. The etiology of TS remains unknown, but new evidence from genetic and neuropathological studies has led to plausible hypotheses for the etiology of some forms of this disorder. The discovery of novel medications for TS, and the assessment of new hypotheses for its causes, has been limited by the paucity of animal models for TS. Existing animal models are based primarily on decades-old measures of "tic-like" or stereotyped behaviors in rats that may have little neurobiological relevance to the most functionally impairing TS symptoms. Most of these antiquated models are limited in their ability to predict efficacy for compounds other than dopamine D2-receptor antagonists, which have only limited efficacy in treating TS. Novel TS models are needed that are sensitive to neurobiological substrates of the most impairing cognitive and sensorimotor deficits in this disorder. The goal of the present application is to develop and apply a novel predictive animal model for TS based on visuospatial priming (VSP) deficits in TS patients. The VSP paradigm is a quantitative psychophysiological measure of response inhibition and facilitation in which TS patients exhibit excessive facilitation and deficient inhibition, relative to healthy controls. VSP deficits in TS patients correlate significantly with the therapeutic outcome of habit reversal therapy, an effective controlled treatment for TS. This suggests that an animal model of VSP deficits may be a valuable and predictive model for novel TS therapeutics. A rat operant model of VSP is being developed that reproduces the patterns of normal VSP exhibited by humans. Rats are trained to respond to a target stimulus, but to inhibit responding to a simultaneously presented distracter stimulus. This discrimination task is then extended to model a full human VSP task, with prime and probe trials and measurements of reaction times to detect levels of facilitatory and inhibitory priming. Normal VSP performance will then be challenged pharmacologically, using drugs that are conceptually linked to neurochemical abnormalities in TS patients. The predictive validity of this novel model will first be assessed using "known" anti-tic medications to normalize VSP deficits, and a potential new medication for TS will then be tested that is believed to function via a novel therapeutic mechanism. Future studies will investigate the neural mechanisms regulating VSP in rats, and will use this measure to test novel genetic and neurodevelopmental hypotheses of TS etiology. If successful, the present application may provide a critical tool to bridge a significant gap in TS research, and ultimately advance our understanding and treatment of this disorder. PUBLIC HEALTH RELEVANCE: The goal of the present application is to develop and apply a novel predictive animal model for Tourette Syndrome (TS) that is based on visuospatial priming (VSP) deficits in TS patients. VSP deficits in TS patients correlate strongly, and highly significantly, with the therapeutic outcome of habit reversal therapy (HRT), an emerging and clinically controlled treatment form for TS. This suggests that a model of VSP deficits in rats may be valuable in predicting therapeutic success in TS, and ultimately help bridge the translational gap from preclinical studies to novel therapeutics for TS.